Eye Colour

eye colour, heritable phenotypic (observable) trait determined by pigmentation and light scattering in the iris of the eye. The iris is a ring of muscle and collagen fibres around a central opening, known as the pupil, through which light passes. The colour of the iris is commonly described by simple terms, such as blue, gray, green, hazel, or brown. However, eye colour varies across a continuous spectrum, such that formal classification schemes for eye colour range from simple three-colour systems to considering multiple colours within one eye. Eye colour is also affected by the variable light available in the environment, resulting in different perceptions of an individual’s eye colour.

The most common colour of iris pigmentation is brown; global estimates suggest that about 79 percent of individuals have brown eyes. The global estimate for the percentage of persons with blue eyes is about 10 percent of the population, the percentage of persons with hazel eyes about 5 percent, and the percentage of persons with green eyes about 2 percent. The incidence of each eye colour varies geographically and in subpopulations.